Steam generator system



July 19, 1966 G. M. EGART 3,261,331

STEAM GENERATOR SYSTEM Filed Oct. 11, 1963 5 Sheets-Sheet 1 Passxwrz4/4: 53mm:

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STEAM GENERATOR SYSTEM Filed Oct. 11, 1963 5 Sheets-Sheet 4 gym/ 3W0 Y-We 27?! July 19, 1966 e. M. EGART 3,261,331

STEAM GENERATOR SYSTEM I5 20 CA R5 United States Patent 3,261,331 STEAMGENERATOR SYSTEM George M. Egart, 202 N. Merrill, Park Ridge, Ill. FiledOct. 11, 1963, Ser. No. 315,587 16 Claims. (Cl. 122448) This inventionrelates to a steam generator system and particularly to such a systemwherein the boiler or steam generator is of the rapid response type.

Steam generators of the aforesaid character are widely used in theheating of railway passenger trains and the generator system is carriedon the diesel locomotive and in its operation is intended to generatesteam in a control-led manner such as to maintain the output pressurewithin a predetermined range at the output end of the generator wherethe output is connected to the train steam line. The upper limit of thispredetermined output pres sure range is established in every instancesubstantially below the setting of the safety valve of the system, andmay be adjustably varied according to the number of cars on theparticular train with which a locomotive is associated. Since such steamgenerator systems are designed for a particular maximum capacity, it iscustomary to provide from one to three such steam generators on thoselocomotives that are intended to haul relatively long trains, and forextreme situations a fourth generator is used.

Such a steam generator system has been made by and sold by Vapor HeatingCorporation of Chicago, Illinois, under the name of Vapor-Clarkson steamgenerator, and such steam generator system as made and sold by VaporHeating Corporation, over the last few years at least, have beensubstantially identical in most respects with the steam generator systemshown in C-larkson et a1. Patent No. 2,751,894, patented June 26, 1956.

The Vapor-Clarkson steam generator system is almost universally used ondiesel passenger locomotives in the United States, and while the systemfunctions reasonably well under ideal conditions and when the steam loador the train length are not excessive, many situations have developedwhere proper heating of the associated train can not be attained eventhough enough steam generator capacity is provided. The difiiculty inheating long trains has caused at least one railway to resort toinstallation of one or more steam generators in a rear car of longtrains.

While the maximum steam output of such a conventional system serves as abasic and limit on its train heating capacity, further limiting factorsare imposed, first, by the necessity to maintain, for any particulartrain length, a minimum head end steam pressure which, despiteprogressive line losses and car-by-car steam consumption along the trainline, will assure a rear car line pressure sufficient to heat the rearcar of the train, and second, by related limiting characteristics ofsuch conventional systems which produce an extremely wide variationbetween maximum and minimum steam pressures, that render it impossiblefor the desired maximum steam pressure to be attained when the loadexceeds the low fire output capacity of the boiler.

In other words, the droop in pressure between low fire and high fire issuch that high output cannot be obtained except with low pressures.

The net result of the foregoing limiting characteristics has been thatwhen the load approaches the maximum boiler output, the Vapor-Clarksonsystem tends to operate at an output steam pressure that is near thelower limit of the relatively large basic pressure range required by theice system. Keeping in mind that the upper limit of the basic pressurerange must be set substantially below the setting of the safety valve,such inherent tendency under high load, to operate at a greatly reducedoutput steam pressure, often renders such a conventional generatorincapable of heating the rear cars of a train even though the totalheating load is less than the rated maximum capacity of the generator orgroup of generators.

Thus, the total heating load, and the train length constitute variablesthat may render such a conventional steam generator, or a group of suchgenerators, incapable of heating the rear cars of a train, and a relatedvariable factor that is encountered is the effective area of the trainsteam line. Standard passenger cars in the United States are now beingequipped with 2 /2 inch steam lines, but many passenger cars are stillin use having 2 inch steam lines. Thus for a particular train theeffective or average area of the train steam line may vary, the mostfavorable condition so far as car heating is concerned being provided bya train made up entirely of cars having 2% inch steam lines, and thisvariable has further complicated the problem of attaining satisfactoryheating of passenger trains.

It is the primary object therefore of the present invention to enablethe steamgenerat-ing systems, including those now installed and in useon passenger locomotives and the like, to be operated in a moresatisfactory and a more efficient manner, to the end that the usefulnessof such equipment may be greatly increased, and more satisfactoryheating of passenger trains may be attained.

Other important objects of the invention are to enable the maximumoutput steam pressure in such systems to be readily varied or set, tocontrol the output steam pressure within a relatively narrow andaccurately determined range, to enable this accurately determined steampressure range to be attained in such :a way that-it is not disturbed orappreciably changed when the maximum steam output pressure is adjustedto a different value, and to enable the maximum output steam pressure tobe governed in such a Way and with such certainty as to permit operationof the system at steam pressures relatively close to the setting of thesafety valve of the system.

More specifically it is an object of the invention to enable thegenerator or boiler of such systems to be more fully utilized, and anobject related to the foregoing is to enable the firing of the boiler ofsuch a system to be accomplished more efficiently.- Other objectsrelated to the foregoing are to minimize the periods of low fireoperation of the boiler so as to thereby produce increased efliciencyand more effective utilization of boiler capacity, and to initiate eachburner operation at high fire so as to assure quick response to anindicated demand for steam.

Other and further objects of the present invention will be apparent fromthe following description and claims, and are illustrated in theaccompanying drawings, which, by Way of illustration, show preferredembodiments of the present invention and the principles thereof, andwhat is now considered to be the best mode in which to apply theseprinciples. Other embodiments of the invention embodying the same orequivalent principles may be used and structural changes may be made asdesired by those skilled in the art without departing from theinvention.

In the drawings: 1

FIG. 1 is a schematic view illustrating a steam generator systemembodying the invention;

FIG. 2 is a vertical central sectional view of a control valve that isembodied in the system, the valve being shown in its fully closedposition;

FIG. 3 is a fragmental portion of FIG. 2 showing the valve member in apartially opened position;

FIG. 4 is a view similar to FIG. 3 and showing valve member in its fullyopen position;

FIG. 4 is a view similar to FIG. 3 and showing valve member in its fullyopen position;

FIG. 5 is graph showing a typical pressure drop curve that may beencountered in the steam line of a railway train;

FIG. 6 is a view showing the pressure characteristics of a steamgenerator system embodying the present invention;

FIG. 7 is a graph showing the required head end pressure for trains ofdifferent length and showing the performance characteristics of thepresent generator system as compared with the prior art system; thegraph being based on the use of a 2 /2 inch diameter train line; and

FIG. 7A is a graph similar to FIG. 7 but based on the use of a 2 inchdiameter train line.

For purposes of disclosure the invention is herein illustrated asembodied in a steam generating unit or system 10 which in most of itsdetails is constructed and arraged as shown and described in Clarkson eta1. Patent No. 2,751,894, patented Tune 26, 1956, and in the drawings ofthis application, those elements of the Clarkson et a1. patent that areemployed without material change have been shown exactly as they wereshown in the aforesaid prior patent. With respect to such elements ofthe system which may be identical with the Clarkson et al. disclosure,and with respect to the general theory of operation thereof, referenceis made to the Clarkson et a1. patent, and such disclosure isincorporated by reference herein as a part of the present disclosure.

Thus, FIG. 1 of the drawings corresponds almost exactly with FIG. 1 ofthe Clarkson et al. patent with the exception that the valve 41 of suchpatent has been replaced by a control valve V which is utilized tocontrol the basic Clarkson et al. system to produce a different and moreefiicient functioning thereof. In FIG. 1 it will be apparent that thesystem of the present invention em- .tbodies a rapid response boiler Bhaving coils 16 defining a path along which boiler feed water isadvanced so as to be heated by the flue gases from a combustion chamber17. The output from the coils 16 of the boiler B is in the form of wetsteam that is fed through an output line 30 to a steam separator 31 andthe separated liquid in the form of warm water is returned through areturn line 32 and associated connections to the water supply source, aswill be described. The steam output of the steam separator 31 passesthrough a shut-oft" valve 39 to an output line 38 which, in the use ofthe system, is connected to the head end of the main steam line of anassociated train.

The boiler or generator B is supplied with gaseous or liquid fuelthrough a nozzle 18, and air for supporting combustion is supplied froma blower structure 52 under the control of a butterfly valve 52A. Therate of supply of fuel and air to the combustion chamber 17 iscontrolled by a servo unit 24, that is in turn governed by the rate offlow of feed water that is being supplied to the boiler B. The rate ofsupply of feed water is, in turn, governed by the steam pressure at thesteam separator 31, this general governing action having been obtainedin the Clarkson et a1. system by a steam pressure responsive valve 41,while in the present instance such control is obtained by the valve V aswill be described in detail hereinafter. Fuel is supplied to the servounit 24 from a tank 107, and under control of the servo unit 24, is fedthrough a line 59 to the fuel nozzle 18 of the boiler B.

The rate of supply of feed water through the line is controlled, asnoted above, by the valve V and this is accomplished by bypassingvarying proportions of water the the

2- supplied by the feed pump 21, the bypass Water being returned to thesupply tank from the valve V to a return line 43.

In order that the operation of the steam connector system 10 of thisinvention may be better described, FIGS. 5 to 7A have been included inthe drawings to bring out the limiting conditions that must be met by atrain heating system in order to attain proper and satisfactory heatingof a train.

Thus FIG. 5 of the drawings constitutes a graph showing typical trainline pressure drop curves that are representative of the pressure dropthat is encountered in a long train between the lea-ding car and therear car. The curves included in FIG. 5 are calculated rather than beingbased upon test data, and these curves take into account an assumedsteam consumption or load per car as well as the car lengths and theline losses introduced by line size, fittings and the like. As will beapparent, the progressive pressure drop assumes a parabolic form and theline losses for any particular train length become particularly rapidwhere the head end pressure is relatively low. As to curve 50, where thehead end pressure is indicated at 210 lbs. per square inch, the pressuredrop is quite rapid so that at the ninth car in a train, the pressurewould have dropped to 100 lbs. per square inch which is usuallyconsidered to be the minimum pressure that is required for properheating of a car.

Curve 51, as shown in FIG. 5, starts with a head end pressure of 240lbs. per square inch and it is to be noted particularly that the curve51 diverges upwardly with respect to the curve so that throughout acomplete twenty-four car train the steam pressure in the line remainsabove lbs. per square inch. Such a pressure of 100 lbs. per square inchis necessary to provide a margin of safety in case of a sudden pressuredrop in some part of the system.

Even greater improvement is shown by curves 52 of FIG. 5 where the headend pressure is indicated as 290 lbs. per square inch, and in thisinstance through the entire train of twenty-four cars the steam pressureis maintained above 193 lbs. per square inch.

Keeping in mind that the curves are based on an assumed load of 300 lbs.of steam per hour per car, it will be clear that the employment of a 290lb. head end steam pressure would provide a great margin of safety sofar as heating is concerned in the event that weather conditionsincrease the heating load above that assumed in calculating curve 52.Particularly, it is noted that a relatively small increase in head endpressure produces a very marked increase in the available pressure atthe rear end or rear car of a train, and hence it should be observedbroadly that so far as train heating is concerned, operation at a highhead end pressure is particularly desirable.

The data used in plotting the pressure drop curves of FIG. 5 has beenemployed in FIGS. 7 and 7A to plot steam demand and head end pressuredemand curves 53 and 53A which are generally similar, but differ in thatdemand curve 53 is based on a 2 /2 inch diameter train line, whiledemand curve 53A is based on the use of a 2 inch diameter train line. Inboth instances, curves 53 and 53A are based on the assumption that asteam pressure of 100 lbs. per square inch is required at the rear carof a train in order to properly heat the rear car.

it may be noted here that FIGS. 7 and 7A contain further plotted datashowing a performance characteristic of the unit 10 of this inventionand of the prior art Vapor- Clarkson generator unit that is currentlyused as standard equipment on railway passenger locomotives.

As a basis for further discussion of FIGS. 7 and 7A, the graph of FIG. 6requires explanation. FIG. 6 constitutes a comparative graph showing theoperating and pressure characteristics of the pressure unit it? and ofthe prior Vapor-Clarkson steam generator system, the graph being basedon test data obtained by operation of a par- 'cular steam unit in itsoriginal form on a diesel locomotive unit. In numerical and tabulatedform, this test data was as follows:

TABLE I.TEST OF NO. 4740 VAPOR-CLARKSON GENERA- TOR 0N AT & SFLOCOMOTIVE UNIT #542 [Using standard Vapor-Clarkson controls] Pin PlateBurner Low Fire High Fire High Fire Setting Marking Off at Off at On at-*Safety valve setting at 285#.

The pressure readings of Table I are of course based on the particularsteam unit tested, so that different test readings must be expected withother steam units.

TABLE II.TES1 OF NO. 4740 GENERATOR ON AT & SF UNIT #542 [Using by-passregulator valve V and making no change in servo or other adjustments]Steam Air Burner High Pressure Pres- 01f Fire On Setting sure 275 107275 260 235# Safety Valves at 285# 250 91 250 230 200# Maxhnum settinglim- 200 67 200 180 155# ited by safety valve 160 50 165 135 115#setting.

Cycling operation under low load conditions The data shown in Tables Iand II illustrates the recurrent onoff cycling that takes place underconditions where there is no load, or where the load is substantiallyless than the full maximum output of the generating system, and itshould be observed that where such a system is operating fairly close toits full output, it does not cycle through on and off cycles, butmodulates its output as will be described in some detail hereinafter.

The test data shown in Table I has been utilized in the graph of FIG. 6to plot steam generator output pressure against the steam generatoroutput, it being noted that the generator on which the test data ofTable I was obtained had a low fire steam output of 1600 lbs. per hourand a steam output of 4800 lbs. per hour at high fire setting. Thus withrespect to the original Vapor-Clarkson unit the lowest steam outputpressure of 165 lbs. per square inch represents the level at which steamoutput pressure must fall on the tested unit in order to establish highfire operation of the boiler, and this point has been plotted in FIG. 6at 55A and shows that at this point in the cycle of test operation ofthe Vapor-Clarkson generator, the steam output rate first reaches itsmaximum. In the Vap'or-Clarkson data of Table I, the high fire opertioncontinues until the steam pressure reaches 195 lbs. and this value hasbeen plotted in 5513. At this point in the operating cycle theadjustment of the burner toward low fire operation is started and thisadjustment continues until the output pressure reaches 230 lbs. persquare inch, this point being plotted at 55C.

At this point in the cycle, the firing adjustment is held at low fire bywhat is termed the delay adapter that is shown in FIG. 73 of the 1950Vapor Corporation Bulletin No. 2203 Rev. A, this figure being shown onpage 67 of such bulletin. Fundamentally, this delay adapter is in theform of an adjustable friction detent of the over-center type, and inthe unit that was tested, a further increase in output steam pressure of35 lbs. per

square inch was required to move the delay adapter burner has beenturned off as indicated at 55D the steam pressure in every instancestarts to drop, and the delay adapter then iseiTectiVe to preventturning on of the burner until the head pressure has reduced to 230 lbs.per square inch. This relation has been plotted at 55E. When the burnerhas been turned on, as indicated at 55E in FIG. 6, the burner will startto adjust gradually toward its high fire position, it being assumed thatthe load in this instance is greater than the output capacity at lowfire, and such adjustment continue and is caused by a furthersubstantial reduction in output steam pressure, and when the output orhead pressure has fallen to lbs. the burner goes into its high fireoperation as indicated at point 55A, heretofore described. The severalpoints 55A to 55E have been connected by lines to form an operatingcharacteristic curve or loop 55 that Was attained with the conventionalVapor-Clarkson generator above discussed.

The lowest output steam pressure of 165 lbs. plotted at 55A in FIG. 6,constitutes an important limiting characteristic of the conventionalVapor-Clarkson steam generator, and it might be pointed out that wherethe load exceeds the low fire output of 1600 lbs. per hour, theconventional Vapor-Clarkson unit never reaches its shutoff point 55D,but on the contrary modulates between high fire and low fire operationwith a substantial proportion of such operation in the low andintermediate firing ranges.

The operating test data set forth in Table II are based on the tests ofthe unit 10 of the present invention, including the control valve V.This data shows that the burner was turned on at 235 lbs. head pressure,since the burner starts at low fire, this has been plotted at point 56E,in FIG. 6. As will be hereinafter described in some detail, the unit 10almost immediately assumes its high fire setting so that as plotted in56A in FIG. 6, the high fire operation starts while the head pressure isstill at approximately 235 lbs. This high fire operation continues untila head pressure of 260 lbs. has been reached, and this value has beenplotted in 5613 in FIG. 6. The firing rate is then gradually decreasedin response to increase in head pressure up to 285 lbs. where the burnerreaches low fire and is then shut off as plotted at 56D in FIG. 6. Thepoints 56A to 56E have been connected in series in FIG. 6 to provide acharacteristicpressure-output curve or loop 56 for the unit 10 of thisinvention.

It will be noted in the test data included in Tables I and II that thesafety valve setting was 285 lbs. during both tests, and it will befurther noted that the burner-off setting of the valve V was somewhathigher than the shut-off setting of the control valve of theVapor-Clarkson unit. This was deliberate in that the valve V that isemployed under this invention has characteristics of reliability whichenable such a lower safety margin to be adopted. This is primarily dueto the expected and rather uncontrollable variations that occur in theuse of the delay adapter with the bypass control valve of theVapor-Clarkson equipment.

It may be pointed out that most railways now prefer to use an evenhigher safety valve setting of 295 so that the on and off pressures forthe steam generators may be correspondingly increased.

The radically different operation of the unit 10 as thus described,results in an unexpected improvement over the train-heating capabilitiesof the basic Vapor-Clarkson system, and as a basis for description ofthis improved operation, the features of the control valve V and themanner of its association in the basic system will now be described.Thus, as shown in FIGS. 2, 3, and 4, the valve V has a sectional,upright housing 60 comprising a base plate 61, relatively tall main body62, and an upper body 63 that are secured together by means such as capscrews 64. Aligned central bores 62B and 63B are formed re spectively inthe main body 62 and the upper body 63 to slidably receive an elongatedvalve stem 65 which at its upper end projects slidably through andbeyond an upstanding sleeve 163 formed at and integrally on the upperbody 63, and which at its lower end projects into a stepped cylinderformed by a pair of enlarged counterbores 166 and 266.

From the horizontal meeting plane of the body members 62 and 63, theupper body member 63 has an upward counterbore to form an enlarged Waterinlet chamber 163, and the main body 26 has a similar downwardcounterbore defining an enlarged water outlet chamber 162. Radial bores263 and 262 extend from the respective inlet and outlet chambers 163 and162 for connection in the feed Water bypass circuit as will bedescribed.

The adjacent ends of the chambers 162 and 163 have shallow andrelatively large counterbores 362 and 363 which define a mounting pocketfor an annular valve seat member 69 which will be described in furtherdetail hereinafter and which is arranged to receive and cooperate aswill be described, with an enlarged valve head 71 formed integrally withthe valve stem 65. The valve head '76 is urged upwardly toward itsclosed position by an expansive coil spring 71 mounted on the top of theupper body 63 and surrounding and associated with the upper end of thevalve stem 65, as will be described, and at its lower end the valve stem65 has a stepped piston 72 fixed thereto for cooperation with the valvespring 71 in moving the valve head 7 1 between its open and closedpositions. The form and relationship of the valve seat 69 and the valvehead 71) will be described in detail hereinafter.

The stepped piston 72 has its smaller upper end 172 slidable in thecylinder 166 and it has its lower and larger end 272 slidable in thelower cylinder 266. A central bore 72B is extended through the piston 72and is counterbored and threaded at 72T at its lower end. The lower endof the piston extends downwardly through the bore 72B and a locking ring72R recessed into the piston rod 65 is seated in the enlargedcounterbore 723T and is held in place by a plug 7 4 which, in additionto its holding function, also serves a controlling purpose as will behereinafter described.

The smaller upper end 172 of the piston is adapted to A be subjected tosteam pressure, as will be described, and a steam inlet port 75 from theupper end of the cylinder 166 opens laterally through the body 63.

For purposes that will hereinafter be described, in detail, the largerpiston 272 is subjected to a constant but variably adjustable fluidpressure, and this pressure may be supplied through an inlet opening '76that is provided in the base plate 61 so as to open into the lower endof the cylinder 266 near the outer edge of the cylinder. It will benoted that the upper end of the cylinder 266 has a lateral vent opening77 to prevent pressure build up within this space.

According to the present invention, the air or other pres sure fluidthat is furnished to the cylinder 266 is continuously bled off at arelatively low rate, and for accomplishing this, the base plate 61 has aplug 78 threaded therethrough in a central relation, and held inposition by a lock nut 78N. The plug 78 has a hardened steel bolt 80extended through a central passage in the plug, and a nut SUN on thelower end of the bolt holds the bolt 80 in position. It may also benoted that the head of the bolt 80 engages a resilient ring 81 to holdthe same in position in a recess 78R in the plug 78. The bolt 86 has acentral passage 82 extended therethrough which may be reduced at itsupper end as at 82R, and this passage constitutes the bleed passage fromthe cylinder 266.

The bleed passage 82 is open or effective at all times except when thepiston 272 is at the lower end of its stroke and when this conditionprevails, an annular sealing ring 85 formed centrally and in adownwardly facing relationship on the nut 74, engages the resilient ring81 so as to close the vent or bleed passage 82 and thus isolate apredetermined central area of the lower face on the piston 272 from theupward force of the pressure fluid in the cylinder 266. The functioningof the piston 272 and its 8 related parts in the operation of the steamgenerator 10 will be described in detail hereinafter.

The spring 71, at its lower end, surrounds the threaded sleeve 163 andbears downwardly against a suitable screw threaded collar 86, thiscollar having a lock screw 86L associated therewith for locking thecollar 86 in adjusted position. The upper end of the piston rod 65 has auniversal coupling 87 associated therewith at one end by means includinga screw threaded connection and a lock nut 87, and the upper or otherend of the universal coupling is similarly associated with an upper bolt88. The bolt 88 has a collar 89 thereon which engages the upper end ofthe spring 71, and a ball thrust bearing 90 rests in place on the top ofthe washer 89 and is secured in this position by a nut and washerarrangement 91.

The valve spring 71 acts to urge the valve head 70 toward itsvalve-closing position, and the line 40 from the steam separator isconnected to the steam inlet passage 75 for applying the output steampressure to the piston 172. It is this steam pressure that urges thevalve head 70 in a valve opening direction. Such movement of the valvehead 70 controls the bypass flow of said water from the line 25 and tothis end, the water inlet passage 263 is connected to the line 23 by aline 42 and the water outlet passage 262 is connected by a line 43 todirect the bypass water back to the supply tank 20.

The valve stroke in the present valve V is limited in extent byengagement of the annular flange or ring 85 with the resilient ring 31at the bottom of the pressure air cylinder 266, and in the presentinstance adjustment of the plug 78 may be employed to vary this maximumstroke of the valve head within a small range of adjustment.

In the embodiment shown herein and as used in the tests describedhereinabove, the valve head 70 moves through a downward opening strokethat includes a first and major portion of its stroke wherein theeffective valve opening is increased very gradually, this portion of thestroke being in the present instance. Further downward movement ofsubstantially produces a rapid increase in the effective valve opening,and thereafter in any further movement up to about /2", the downwardmovement of the valve head 70 may be considered as an idle movement inthat no further increase in the effective valve opening is caused.

As above pointed out, the steam pressure from the steam separator actson the upper end of the piston 172 so as to tend to compress the spring71 and open the valve V, and under the present invention, as will bedescribed in further detail hereinafter, this valve opening forceapplied by the steam pressure is opposed by the resilient action ofpressure air in the cylinder 266 which acts upwardly on the piston 272.Thus, the valve closing forces in this instance are provided by thesubstantially constant force of the spring 71 coupled with the forceprovided by the pressure air which of course may be adjusted or variedto thus provide for adjustment of the operating points of the valve V.Thus the air pressure within the cylinder 266 is provided from a source94 and connecting pipes 95 and 95A, a pressure regulating valve 96 beingprovided between the lines 95 and 95A for adjustably varying the airpressure that is supplied to the cylinder 266. The regulating valve 26may of course be located remotely with respect to the unit 10, and hencethe heater operation may be controlled from the locomotive cab. Itshould be noted that selecting a specific air pressure reading onregulating valve 96 will effectively establish the operating steampressure of the steam generator. Thus the air pressure regulator 96 iscalibrated to read steam pressure directly.

With the arrangement thus provided the spring 71 operates at all timeswithin a limited range of compression and this range of compression isthe same regardless of the value of the air pressure established in thecylinder 266. Basically, the spring 71 is relatively long and relativelysoft and in a valve V of the dimensions and stroke above specified, atwo inch spring about seven inches long and having a spring rate ofabout 119 lbs. per inch may be employed to produce the desiredoperation. With such an arrangement and with the piston 172 having adiameter of about 2 /2, the valve head 70 may be moved throughout itsentire range in response to a steam pressure variation of about lbs. andthe operation of the spring 71 is the same, no matter what theadjustment of the air pressure may be. In this connection it is pointedout that the area of the piston 272 that is subjected to air pressurein' the present instance is twice the area of the piston 172 that issubjected to steam pressure, and hence a lower air pressure may beemployed.

In the particular valve that was used in obtaining the test data uponwhich FIG. 6 of the drawings is based, the air pressure in the cylinder266 was adjusted so that the valve head 70 would be moved to its fullyopen position when the steam pressure reached a value of 275 lbs., andat this steam pressure value, the valve head 70 was moved to its fullyopen position wherein the bypass was completely open so that all of theboiler feed water was bypassed, and the burner was consequently shutoff.

When the valve head 70 is in its fully open position, the downwardlyprojecting ring 85 on the piston 272 closes the bleed passage 82, andthis has an important controlling action on the operation of the system.When the bleed passage 82 is closed, the area of the piston 272 that isenclosed within the downwardly projecting ring 85 'is no longersubjected to pressure air that is supplied by the line 95A and theupward resilient forces applied by a piston 272 to the valve member arecorrespondingly reduced in accordance with the area of the piston 272that has thus been described. In the present instance the proportioningof the diameters of the ring 85 and the piston 272 are such that asubstantial further drop in the steam pressure in the cylinder 166 isrequired before the combined action of air pressure and spring pressurecauses the valve head 70 to return to its fully closed position whereinthe burner of the boiler is turned on at high fire. Such closure of thevalve takes place almost instantaneously because as soon as the ring 85is lifted off of its resilient seat 81, the entire lower face of thepiston 272 is again rendered effective so that there is a suddenincrease in the total force tending to close the valve. In the valve Vthat was used in the tests above described, the proportioning of the twodifferent areas of the piston 272 was such that the steam pressure wasrequired to drop to about 235 lbs. per square inch.

The valve head and valve seat In a broad sense, the operation of thevalve head 70 through its downward stroke from the closed position ofFIG. 2 and through the position shown in FIG. 3, and finally to thefully open position of FIG. 4, is such that throughout the movement fromthe FIG. 2 position to the position of FIG. 3, the effective valveopening gradually is increased, and soon after thevalve head 70 passesdownwardly beyond the position shown in FIG. 3, there is a suddenincrease in the effective valve area so that in this situation, thevalve V acts as a complete dump valve to re turn all of the boiler feedwater and thus stop operation of the burner.

As will be evident particularly in FIGS. 3 and 4 of the drawings thevalve seat member 69 has a central cylindrical opening or bore 169through which the valve stem extends, and at its lower end, the bore 169is counterbored to provide a tapered downwardly facing seat 269 that isannular in character. The seat 269 meets the bore 169 in an annular edge369 which becomes important in consideration of the functioning of thevalve as will hereinafter appear. Just above the head 70, the valve stem65 has a reduced diameter portion 165 that is defined by shoulders atits upper and lower ends, and the lowermost of these shoulders definesthe upper end of the valve head 70 in a manner that will be described indetail hereinafter.

The head 70 comprises an enlarged integral portion of the valve stem 65,and the lower portion of the head being the largest, and this lowerportion has its upper edge defined by an annular upwardly facing taperedseat 270 that is complemental to the downwardly facing tapered seat 269.Above the tapered seat 270, the valve head 70 has an upwardly extendedtapered section 170 that meets the inner upper edge of the seat 270along an annular line 270L. The upper end of the section 170 terminatesin an annular corner 370 that is defined by the intersection of thesurface of the section 170 with the shoulder that defines the lower endof the reduced section of the valve stem.

At its lower end, as defined by the annular line 270L, the taperedsection has a diameter that is precisely equal to the diameter of :thebore 169 of the valve seat member 69, and the section 170 tapersgradually toward a smaller diameter at the upper end thereof as definedby the annular edge 370.

Thus when the valve member 70 is in its upper position of FIG. 2, theseats 269 and 270 are engaged and the valve is fully closed, and as thevalve stem 65 is moved downwardly, an annular space is formed betweenthe tapered surface of the section 170 and the annular line 369 of thevalve seat 69. This annular space thus constitutes the effective valveopening, and as the valve stem 65 is moved progressively downwardly,this annular space is gradually increased, as will be evident by acomparison of FIGS. 2 and 3. When the annular upper edge 370 of thevalve head 70 passes the horizontal plane of the annular line 369,continued downward movement causes the effective area of the valveopening to be rapidly increased, and this increase takes place at a ratethat greatly exceeds the rate of increase in the earlier portions of thevalve opening movement. Hence, in the final downward movements of thevalve head 70, as for example from the position of FIG. 3 to theposition of FIG. 4, the effective area between the annular edge 370 andthe annular edge 360 soon exceeds the area between the reduced portion165 of the valve stem and the bore 169. In other words, the ratio ofarea increase with respect to the valve stem movement suddenlyincreases, so that a well defined cut-off point is provided where thesudden dumping of all of the flow from the feed water line causes theburner to be quickly shut off. The point of sudden enlargement of thebypass line effectively establishes the minimum firing rate and preventsfire at a rate below that required for stable combustion.

The movement of the valve member 70, downwardly beyond its fully openposition of FIG. 4 brings the annular member 85 into engagement with theresilient annular member 81, and this immediately reduces the effectivearea of the lower or larger piston 272. The net result of this is that adifferential is established for the valve V so that the steam pressuremust drop a considerable amount before the valve spring 71 will again beable to move the valve head 70 to its closed position. In the presentinstance this differential has been established as requiring a 40 lb.per square inch further decrease in the head'end steam pressure. Thuswhen the pressure has dropped off in the required amount, the spring 71starts gradually to lift the valve stem 65. As soon as the members 85and 81 have been separated to a slight extent, the air pressure in thelower cylinder 266 again becomes effective through out the entire lowerarea of the piston 272 so that additional pressure equal to the 40 lb.differential above-mentioned is immediately applied to the valve stem,and this results in almost immediate upward movement of the valve head70 from its fully open position to its fully closed position. This ofcourse results in a full volume flow of feed water through the servounit so that the burner is quickly adjusted to its high fire positionand the generator starts production of steam at its maximum output rate.

Operation close to maximum output capacity In FIG. 6 of course the fullcycling operation of both the prior system and the system of the presentinvention have been illustrated, and it has been pointed out thatbasically FIG. 6 shows such cycling as it occurs when the systems areworking under no load, or relatively light load. However, when such asystem is working at a load which exceeds or closely approximates themaximum steam output of the system, the operation is quite different inthat the boiler does not go through its off-on cycles, but in contrast,operates close to the maximum output capacity with the flame modulatingbetween high fire and an intermediate fire. This is because under suchconditions, the increase in head steam pressure will cause a gradualreduction in the firing rate, and when the rate of steam productionfalls below the rate of steam consumption, the pressure in the outputline of the system falls so as to tend to increase the firing rate inthe boiler. Thus, with respect to the Vapor-Clarkson system, operationat a level closely approximating the high fire maximum output causes theboiler to modulate within a range such as the range indicated by theshaded area M in FIG. 6. Under such circumstances the boiler will not gooff and on, nor will the output pressure fall below the level 55B to anyappreciable degree.

As applied to the steam generator of this invent-ion, a similarsituation prevails as will be evident in FIG. 6 of the drawings whereinthe modulating area within which the generator operates when the loadclosely approximates the maximum output is indicated by a shaded area Nthat lies immediately below the line 56B56D of FIG. 6.

A comparison of the Vapor-Clarkson operation and the operation of thegenerator 10 of this invention shows that under such modulatingope-ration of the Vapor-Clarkson unit may have its output pressurereduced to something below 200 lbs. per square inch, while in the unitof this invention the modulating operation of the unit maintains a muchhigher minimum output steam pressure that, in the selected example, isabove 260 lbs. per square inch.

The improved heating of long trains In FIGS. 7 and 7A such operation ofthe Vapor-Clarkson unit and the ope-ration of the steam generator ofthis invention have been plotted against the steam demand curvepresented in trains of ditferent lengths, FIG. 7, showing thisrelationship where a 2 /2" train line is used while FIG. 7A shows thisrelationship where a 2" train line is employed.

Thus, in FIG. 7, the output of a single Vapor-Clarkson unit has beenillustrated by the line 1-55 which at its opposite ends is determined byplotting the points 55E and 55B of the Vapor-Clarkson operation asillustrated in FIG. 6. Similarly, a line 2 55, and a line 3-55 have beenillustrated in FIG. 7 showing the output capacity of two Vapor-Clarksonunits and three Vapor-Clarkson units, respectively, and these merelyserve to add the output of the indicated number of individual steamgenerating units.

Similarly, the line 156 and the line 2-56 have been plotted on FIG. 7 toshow the output capacity of one unit 10 of this invention, and two units10 of this invention.

FIG. 7A has the output capacity of the steam generating units plottedthereon in the same general manner as in FIG. 7.

Thus, it will be clear for example in FIG. 7 that with the steam demandcurve 53 as plotted therein, the maximum number of cars that can beheated by a single Vapor- Clarkson unit is but 16 cars, and this samelimitation is resent with respect to the steam generating units 10 ofthe present invention, it being noted that in both instances thelimitation is produced by the maximum capacity of the steam generatorsrather than by the steam line. When more than one generator is employed,however, the situation is radically different. Thus, when twoVapor-Clarkson units are employed, the output capacity is such that I2the two uni-ts will heat more than 16 cars, but because of therelatively low pressure that is attainable with the Vapor-Clarksonunits, the maximum capacity is 21 cars.

Even where a third Vapor-Clarkson steam generator is added, there is buta slight increase in the steam pressure so that three suchVapor-Clarkson generators will have no greater heating capacity on thetrain than the two Vapor-Clarkson units. In other words, even with threeVapor-Clarkson units, only 21 cars can be heated.

In contrast to this then it should be noted that where two units It]! ofthis invention are employed, the output capacity and the output pressurecharacteristics are such that 26 cars may be effectively heated.

Similarly, as shown in FIG. 7A, the unit 10 of this invention enablesgreater efficiency to be attained even when a 2" trainline is used.

Thus, the low output pressure of a single Vapor-Clarkson unit will heatbut 13 cars, while a single unit It) of this invention will heat 16 carsand is limited only by the maximum output of the unit.

Where two steam generators are used, the units 10 will heat 18 cars,while two Vapor-Clarkson units will heat but 15 units; the limitation ineach instance being imposed by pressure drop in the trainline.

Conclusion From the foregoing description it will be apparent that thepresent invention enables steam generating systems of the kind now usedin passenger locomotives and the like to be operated in a moresatisfactory and efiicient manner so that the usefulness of suchgenerating systems is increased and passenger trains may be heated withgreater effectiveness. It will also be apparent that the presentinvention enables the maximum steam output pressure in such systems tobe readily varied or set, and it also enables the output steam pressureto be controlled within relatively narrow and accurately determinedlimits.

It will also be evident that the present invention enables the maximumsteam output pressure to be governed in such a way in railway steamgenerating units that the maximum output pressure of such systems may beset relatively close to the setting of the safety valves in the systems.It will further be evident that the present invention enables thegenerator or boiler of such steam generating systems to be utilized withgreater etficiency than has been possible heretofore, and as a furtherpoint, the firing of the boiler is accomplished under the presentinvention with greater efiiciency.

It will also be apparent that the present invention makes it possible tominimize the periods of low fire operation in steam generators of thekind used in railway work for heating purposes and because low fireoperation is minimized, the boiler capacity is utilized more effectivelyand more effioiently.

It will also be apparent that under the present invention the burner isimmediately adjusted to its high flame operation when the burner isstarted, and therefore, steam production is attained relatively early inthe cycle at the maximum output rate of the unit.

Thus while a preferred embodiment of the invention has been illustratedherein, it is to be understood that changes and variations may be madeby those skilled in the art without departing from the spirit and scopeof the appended claims.

I claim:

1. In a steam generating system having a boiler with a fluid fuel burnerand a feed water line for the boiler having a constant rate feed waterpump discharging to said feed water line, burner control means includinga fuel valve for turning the burner on or off and varying the firingrate thereof between low fire and high fire operation, servocontrolmechanism through which said feed water line is connected and responsiveto the fiow rate of feed water through said servo mechanism to saidboiler to govern said burner control means to turn the burner oif inresponse to feed water flow rates below a predetermined minimum feedwater flow rate and to turn the burner on in response to a feed waterflow greater than said predetermined minimum feed water flow rate andWhile the burner is on to vary the firing rate of the burner insubstantially direct proportion to the feed water flow rate, a bypassline connected to said feed Water line between said feed pump and saidservo mechanism and through which varying proportions of the feed watermay be bypassed, and control valve means variably governing said bypassline and responsive in recurrent variations in the steam output pressureof said boiler, said control valve means including means responsive to apredetermined maximum steam output pressure to fully open said bypassline to thereby reduce the feed water flow rate to a value below saidminimum flow rate to thereby shut off said burner, means for graduallyopening said control valve means in responsive to increases in saidoutput steam pressure until said maximum output steam pressure isreached, and means for maintaining said bypass line fully open when saidmaximum steam output pressure is reached and until said output steampressure falls to a predetermined minimum output pressure whilethereafter immediately fully closing said control valve to thereby causemaximum flow of feed water to the servo unit and immediate operation athigh fire.

2. In a steam generating system having a boiler with a burner forburning fluid fuel and a liquid supply line for supplying water to theboiler, means for pumping said water at a constant rate through saidsupply line, a servo unit actuated by the flow rate of the feed water ata particular point in said supply line to vary the supply of fuel indirect proportion to the variations in the flow rate of the feed waterat said point in said supply line, and means responsive to the outputsteam pressure of the boiler to bypass said water from said supply linebefore it reaches said point for varying the flow rate of feed water atsaid point, said last-mentioned means comprising a valve member having aspring normally urging said valve member toward said closed position andmeans associated with the valve member and responsive to steam pressurefor imparting movement to the valve member in an opening direction,piston and cylinder means associated with said valve member for applyingresilient force to the valve member in the same direction as saidspring, a source of air under pressure, means including a variablysettable pressure reducing valve for applying pressure airto said pistonand cylinder means, said valve member being formed to gradually increasethe effective area of the valve opening as the valve member is moved inan opening direction, and in the final portion of the opening stroke ofthe valve member, being arranged to rapidly increase the effective valveopening.

3. A steam generating system according to claim 2 in which said pistonand cylinder device has a bleed opening for gradual bleeding pressureair from the cylinder and said piston having means thereon effectivewhen the valve member is in its fully open position to close said bleedopening and isolate a substantial area of the piston from the airpressure within said cylinder.

4. In a steam generating system having a boiler with a burner forburning fluid fuel and a liquid supply line for supplying said water tothe boiler, means for pumping said water at a constant rate to saidsupply line, a servo unit actuated by the flow rate of the feed water ata particular point in said supply line to vary the supply of fuel indirect proportion to the variations in the flow rate of the feed waterat said point in said supply line, and means responsive to the outputsteam pressure of the boiler to bypass said water from said supply linebefore it reaches said point for varying the flow rate of feed water atsaid point, said last-mentioned means comprising a control valve havinga valve body having inlet and outlet chambers with an intermediate valveport, a valve member cooperating with said port and movable in one ofsaid chambers between open and closed positions, said valve member beingformed to gradually increase the effective area of the valve opening asthe valve member is moved in an opening direction, and in the finalportion of the opening stroke of the valve member, being arranged torapidly increase the effective valve opening; resilient means urgingsaid valve member toward closed position, steam pressure responsivemeans for moving said valve member from closed position toward openposition in amounts substantially proportional to the increase of suchsteam pressure between a predetermined intermediate level and apredetermined maximum level, and differential producing means modifyingthe action of said resilient means for maintaining the valve member inits fully open position until the steam pressure has decreased to apredetermined minimum level substantially below said intermediate leveland to thereupon immediately close said valves.

5. In a steam generating system having a boiler with a burner forburning fluid fuel and a liquid supply line for supplying said Water tothe boiler, means for pumping said water at a constant rate to saidsupply line, a servo unit actuated by the flow rate of the feed Water ata particular point in said supply line to vary the supply of fuel indirect proportion to the variations in the flow rate of the feed waterat said point in said supply line, and means responsive to the outputsteam pressure of the boiler to bypass said water from said supply linebefore it reaches said point for varying the flow rate of feed water atsaid point, said last-mentioned means comprising a control valve havinga valve body having inlet and outlet chambers with an intermediate valveport, a valve member cooperating with said port and movable in one ofsaid chambers between open and closed positions, said valve member beingformed to gradually increase the effective area of the valve opening asthe valve member is moved in an opening direction, and in the finalportion of the opening stroke of the valve member, being arranged torapidly increase the effective valve opening; resilient means urgingsaid valve member toward closed position, steam pressure responsivemeans opposing said resilient means for adjusting said valve member fromclosed position toward said open position by valve movements that varydirectly with increase of the steam pressure from a predeterminedintermediate level to a predetermined maximum level, and means formaintaining the valve member in its open position until the steampressure falls below said intermediate level to a predetermined minimumlevel and to thereupon immediately close said valve.

6. In combination with a steam generating system of the kind in whichthe fuel and air supply is governed in response to the rate of feedwater flow to the boiler, and in which the rate of feed water flow tothe boiler is varied by variably by-passing all or part of a constantfeed water flow in a feed Water supply circuit, a bypass control valvehaving a valve member movable between open and closed positions and aspring urging the valve member to closed position, said valve memberbeing formed to gradually increase the effective area of the valveopening as the valve member is moved in an opening direction, and in thefinal portion of the opening stroke of the valve member, being arrangedto rapidly increase the effective valve opening, piston and cylindermeans connected to the output steam pressure of the boiler for applyingopening force to the valve member, piston and cylinder means forapplying closing force to said valve member, and means including avariably settable pressure reducing valve for applying pressure aid tosaid last-mentioned piston and cylinder means.

7. The combination defined in claim 6 wherein means are provided forreducing the force applying effectiveness of said last-mentioned pistonand cylinder means while said valve member is in its fully openposition.

8. The combination defined in claim 6 wherein movement of said valvemember to its open position partially disables said last-mentionedpiston and cylinder means.

9. In a bypass control valve for use in the bypass of the feed Watersupply line of a steam generator, a valve body having a valve chamberwith inlet and outlet passages and a valve port within the chamberbetween said passages, a valve member in said chamber movable betweenopen and closed positions with respect to said valve port, said valvemember being formed to provide a gradual increase in the effective valveopening as the valve member moves from closed position to substantiallyits open position and then to rapidly increase such effective area asthe valve member completes its movement to said open position, steampressure responsive means for urging said valve member toward openposition, a valve spring urging said valve member to closed position andair pressure responsive means for supplementing the force of the springin urging said valve member toward closed position.

10. A control valve according to claim 9 wherein means are provided forreducing the efiectiveness of the air pressure responsive means whilethe valve member is in its open position.

11. In a bypass control valve for use in the bypass of the feed watersupply line of a steam generator, a valve body having a valve chamberwith inlet and outlet passages and a valve port within the chamberbetween said passages, a valve member in said chamber movable betweenopen and closed positions with respect to said valve port, said valvemember being formed to provide a gradual increase in the effective valveopening as the valve member moves from closed position to substantiallyits open position and then to rapidly increase such effective area asthe valve member completes its movement to said open position, doubleacting piston and cylinder means connected to said valve member andhaving a small piston and a large piston respectively subjectable todifferent pressure sources thereby to be subjected to steam pressure forurging the valve member to ope-n position and to air pressure for urgingthe valve member to closed position.

12. In a steam-pressure actuated bypass control valve for the feed watersupply system of a steam generator, a valve body having inlet and outletchambers with an intermediate valve port, a valve member cooperatingwith said port and movable in one of said chambers between open andclosed positions, said valve member being formed to gradually increasethe effective area of the valve opening as the valve member is moved inan opening direction, and in the final portion of the opening stroke ofthe valve member, being arranged to rapidly increase the effective valveopening, resilient means urging said valve member toward closedposition, steam pressure responsive means for moving said valve memberfrom closed position toward open position in amounts substantiallyproportional to the increase of such steam pressure between apredetermined intermediate level and a predetermined maximum level, anddifferential producing means reducing the force of said resilient meansfor holding the valve member in fully open position until the steampressure has decreased to a predetermined minimum level substantiallybelow said intermediate level and for then immediately moving said valvemember to fully closed position.

13. In a bypass control valve for use in the bypass of the feed watersupply line of a steam generator, a valve body having a valve chamberwith inlet and outlet passages and a valve port within the chamberbetween said passages, a valve member in said chamber movable betweenopen and closed positions with respect to said valve port, said valvemember being formed to provide a gradual increase in the effective valveopening as the valve member moves from closed position to substantiallyits open position and then to rapidly increase such effective area asthe-valve member completes its movement to said open position, resilientmeans including a valve spring for yieldingly urging the valve member toclosed position, steam pressure responsive means opposing said resilientmeans for adjusting said valve member from closed position toward saidopen position by valve movements that vary directly with increase of thesteam pressure from a predetermined intermediate level to apredetermined maximum level, and means for maintaining the valve memberin its open position until the steam pressure falls below saidintermediate level to a predetermined minimum level, and for thenapplying a substantial resilient valve closing force to immediately movethe valve member to closed position.

14. In a control valve, a valve body having a valve chamber with inletand outlet passages and a valve port within the chamber between saidpassages, a valve member in said chamber movable between open and closedpositions with respect to said valve port, said valve member beingformed to provide a gradual increase in the elfective valve opening asthe valve member moves from closed position to fully open position,pressure means for biasing said valve member toward its open position,and two-stage biasing means for opposing the action of said pressuremeans, said biasing means being formed to apply a predetermined amountof biasing force in a first stage of operation when said valve member isin said fully open position and to apply an increased amount of biasingforce in all other positions of said valve member, thereby allowing aholding action of said valve member in said open position until saidpressure means falls to a predetermined level.

15. A valve as set forth in claim 14 wherein said twostage biasing meansincludes a spring interconnected with said valve member to move ittowards closed position, and air pressure means for biasing said valvemember toward closed position, and means for reducing the effectivenessof said air pressure means when said valve member is in its fully openedposition.

167 The valve as set forth in claim 14 wherein said two-stage biasingmeans includes a regulated source of air pressure.

References Cited by the Examiner UNITED STATES PATENTS 2,834,569 5/1958Nickerson 25 l62 3,029,060 4/ 1962 Anderson 25 l-62 3,105,468 10/1963Gardham l2245l FREDERICK L. MATTESON, 111., Primary Examiner.

C. R. REMKE, Assistant Examiner.

2. IN A STEAM GENERATING SYSTEM HAVING A BOILER WITH A BURNER FORBURNING FLUID FUEL AND A LIQUID SUPPLY LINE FOR SUPPLYING WATER TO THEBOILER, MEANS FOR PUMPING SAID WATER AT A CONSTANT RATE THROUGH SAIDSUPPLY LINE, A SERVO UNIT ACTUATED BY THE FLOW RATE OF THE FEED WATER ATA PARTICULAR POINT IN SAID SUPPLY LINE TO VARY THE SUPPLY OF FUEL INDIRECT PROPORTION TO THE VARIATIONS IN THE FLOW RATE OF THE FEED WATERAT SAID POINT IN SAID SUPPLY LINE, AND MEANS RESPONSIVE TO THE OUTPUTSTEAM PRESSURE OF THE BOILER TO BYPASS SAID WATER FROM SAID SUPPLY LINEBEFORE IT REACHES SAID POINT FOR VARYING THE FLOW RATE OF FEED WATER ATSAID POINT, SAID LAST-MENTIONED MEANS COMPRISING A VALVE MEMBER HAVING ASPRING NORMALLY URGING SAID VALVE MEMBER TOWARD SAID CLOSED POSITION ANDMEANS ASSOCIATED WITH THE VALVE MEMBER AND RESPONSIVE TO STEAM PRESSUREFOR IMPARTING MOVEMENT TO THE VALVE MEMBER IN AN OPENING DIRECTION,PISTON AND CYLINDER MEANS ASSOCIATED WITH SAID VALVE MEMBER FOR APPLYINGRESILIENT FORCE TO THE VALVE MEMBER IN THE SAME DIRECTION AS SAIDSPRING, A SOURCE OF AIR UNDER PRESSURE, MEANS INCLUDING A VARIABLYSETTABLE PRESSURE REDUCING VALVE FOR APPLYING PRESSURE AIR TO SAIDPISTON CYLINDER MEANS, SAID VALVE MEMBER BEING FORMED TO GRADUALLYINCREASE THE EFFECTIVE AREA OF THE VALVE OPENING AS THE VALVE MEMBER ISMOVED IN AN OPENING DIRECTION, AND IN THE FINAL PORTION OF THE OPENINGSTROKE OF THE VALVE MEMBER, BEING ARRANGED TO RAPIDLY INCREASE THEEFFECTIVE VALVE OPENING.